So many people saying sell sell - I say don't sell... the S15 runs a SR20 - that's a 4 cylinder 2.0 litre turbo versus a 2.5 litre 6 cylinder turbocharged Skyline... the S15 looks hideous and is piss weak... sure, some are heavily modified and yes, mods vs mods etc - but trust me, stock for stock - jump in a S15 Silvia and you will regret it - you will feel a power drop for sure.
But yes, S15 is newer and does look slick as well - I do like their interior but looks-wise, a R33 rules imo.
I would never get a S15.
If I were to upgrade, R33 GTR full stop.