1500g wheels for under £400 buying new isn’t going to happen without serious compromises.
Hunt or Silt are the best bet, but the compromise is narrowish (but ok) internal width rims, narrow gauge spokes, paper thin rim tape (Hunt), alu nips and living with a few dings now and then.
The good news is both offer crash replacement policies which I have made use of with Hunt when a stick ripped spokes through the rim and for a rim dent.
If you want to spec your own wheels then maybe use a site like R2 bike to see real world weights and decent prices. The breakdown of my Hunt XC Wide wheelset may help understand how the various parts contribute to the final weight
Pair Boost Hunt XC Wide with valves and Stans rim tape: 1672g
Rims: 440g and 452g
Front hub: 156g
Rear hub (HG freehub): 283g
Spokes and nipples: 316g
Rim tape (Stans): 17g
Valves (Hunt pair): 8g