Why do new mods run slow?

[Skorzeny8814]

I have a lot of F1 mods for rFactor but the new ones (especially F1 2015) runs very slow and laggy on the same settings as F1 RFT 2010 runs smooth without any lag. I tried to reduce the new mods textures resolutions but it doesn't help at all. It's strange cause I don't even see any difference in the details of F1 RFT 2010 and F1 WCP 2015 for example. What can cause the problem?