RPF1 are readily available.. 949 Racing 6ULs are also very light (5.2 kg in 15x7).
The TD Pro Race 1.2 wheels are excellent for the money but just over 6KG. TBH, though, they're a strong design and cheap in the UK and popular with UK racers for great reasons.
www.racerindustries.com.au/afawcs0161690/CATID=26/ID=15138/SID=30024495/Team-Dynamics-Pro-Race-1.2.htmlI saw a set of CE28N for sale on Ebay recently, 15x6.5 but still excellent wheels and crazily light weight.
Here's a list of the 15x7 wheels by weight.. lightest at the top, those under 6kg.. - this isn't really a complete list as new wheels come along.
wheel - method of manufactur, size, lbs, kgs
Volk CE28N Forged 15x7 9.1 4.12769084
SSR Type-C (called Competitions in the US) Forged 15x7 9.2 4.17305008
Volk TE37 Forged 15x7 9.2 4.17305008
Racing Hart CP-035R Forged 15x7 9.4 4.26376856
Enkei RP-F1 Cast 15x7 9.8 4.44520552
Kyoho Tracer Cast 15x7 9.9 4.49056476
Starform Real Racing R2 Forged 15x7 9.9 4.49056476
Buddy Club P1 Racing QF Forged 15x7 10.1 4.58128324
KMS Superlight Forged 15x7 10.1 4.58128324
RS Watanabe EightSpoke F8 Cast Mg 15x7 10.1 4.58128324
AME Tracer TSSC Cast 15x7 10.2 4.62664248
BBS RG F1-Racing (Japan Only) Forged 15x7 10.2 4.62664248
BBS RG-F Forged 15x7 10.2 4.62664248
Motegi Racing Trak Lite 2 Forged 15x7 10.3 4.67200172
RS Watanabe Cyclone Forged Mg 15x7 10.4 4.71736096
Minilite Magnesium Forged Mg 15x7 10.5 4.7627202
5Zigen Beckets FN-01R Forged 15x7 10.6 4.80807944
Wed's TC-005 Forged 15x7 10.7 4.85343868
Motegi Racing Trak Lite Forged 15x7 10.8 4.89879792
5Zigen Copse Cast 15x7 11 4.9895164
Enkei ES-Tarmac Cast 15x7 11 4.9895164
Mugen MF10L Forged 15x7 11 4.9895164
RS Watanabe EightSpoke F8F Cast Mg 15x7 11.2 5.08023488
Volk TE37 Gravel Forged 15x7 11.2 5.08023488
Wed's TC-105N Forged 15x7 11.2 5.08023488
SJ Racing Leggero Forged 15x7 11.3 5.12559412
Advan Racing RG Cast 15x7 11.4 5.17095336
Falken Hanabi Cast 15x7 11.5 5.2163126
OZ Superleggera Cast 15x7 11.5 5.2163126
RS Watanabe EightSpoke F8FS Cast Mg 15x7 11.7 5.30703108
RS Watanabe Forged Eight Forged 15x7 12.1 5.48846804
Circle Racing Series 82 Spun 15x7 12.2 5.53382728
SSR MK-III Forged/Spun 15x7 12.2 5.53382728
ATS DTC Motorsport Cast 15x7 12.3 5.57918652
Drag Wheels DR9 Cast 15x7 12.3 5.57918652
OZ Ultraleggera Cast 15x7 12.4 5.62454576
Konig Britelite Cast 15x7 12.5 5.669905
Motegi Racing LC5 Cast 15x7 12.5 5.669905
SSR Schumacher Forged/Spun 15x7 12.5 5.669905
Axis Mag-Lite Cast 15x7 12.6 5.71526424
Kosei K1 TS Cast 15x7 12.6 5.71526424
Real Racing Cast 15x7 12.7 5.76062348
Rota Speed 5 Cast 15x7 12.7 5.76062348
Drag Wheels DR21 Cast 15x7 12.9 5.85134196
Rota Slipstream Cast 15x7 12.9 5.85134196
A-Tech Finalspeed Cast 15x7 13 5.8967012
Blitz Type 02 Forged/Spun 15x7 13 5.8967012
Enkei RPO-2J Cast 15x7 13 5.8967012
Rota J-MAG Cast 15x7 13 5.8967012
Enkei J-Speed III Cast/Spun 15x7 13.2 5.98741968
Volkswagen Golf GTI (BBS RS 3-piece) Forged/Cast 15x7 13.2 5.98741968
Konig Network Cast 15x7 13.4 6.07813816
Stern Aguzze-S07 Cast 15x7 13.4 6.07813816
Team Dynamics Pro Race 1 Cast 15x7 13.4 6.07813816
Gram Lights 57C Cast 15x7 13.5 6.1234974
Kosei K1 Racing Cast 15x7 13.5 6.1234974
MB Motoring Competition Cast 15x7 13.5 6.1234974
OZ Crono HT Cast 15x7 13.5 6.1234974
Rota GT-3 Cast 15x7 13.5 6.1234974
Stern Mach III Cast 15x7 13.5 6.1234974
Kosei RT Penta Cast 15x7 13.8 6.25957512
Superlight Billet Billet/Spun 15x7 13.8 6.25957512
Hayashi Street Wheel Type STF Cast 15x7 13.9 6.30493436
5Zigen FN01R-C Cast 15x7 14 6.3502936
Centerline Neutron Forged 15x7 14 6.3502936
Konig Next Cast 15x7 14 6.3502936
Team Dynamics DTM Cast 15x7 14 6.3502936
Team Dynamics Pro Race 2 Cast 15x7 14.1 6.39565284
BBS RK Cast 15x7 14.2 6.44101208
Enkei RPO-1 Cast 15x7 14.3 6.48637132
Rota RB Cast 15x7 14.4 6.53173056
Advan Racing Oni Cast 15x7 14.5 6.5770898
ASA LW5 Cast 15x7 14.5 6.5770898
Enkei RCT-1 Cast 15x7 14.5 6.5770898
Motegi Racing SP10 Cast 15x7 14.5 6.5770898
Konig Rewind Cast 15x7 14.6 6.62244904
RS Watanabe EightSpoke F8F Cast 15x7 14.6 6.62244904
BBS RX Cast 15x7 14.7 6.66780828
Enkei RS+M Cast 15x7 14.8 6.71316752
Konig Kolors Cast 15x7 15 6.803886
ROH Snyper Cast 15x7 15 6.803886
Sportmax 002 Cast 15x7 15 6.803886
Team Dynamics Qualifier Cast 15x7 15 6.803886
Weld Type 76 Forged 15x7 15 6.803886
Work Emotion CR Kai Cast 15x7 15 6.803886
Drag Wheels DR20 Cast 15x7 15.2 6.89460448
Enkei RPO-2 Cast 15x7 15.2 6.89460448
Chaparral S 15 Cast 15x7 15.3 6.93996372
Revolution RFX Race Cast 15x7 15.3 6.93996372
Esses SpeedMaster SM-058 Cast 15x7 15.4 6.98532296
Superlight Ultralight Cast/Spun 15x7 15.4 6.98532296