The differences between this modpack vs Prehistoric fossils is that we don't have Prehistoric Nature Decorations mod which is PC-heavy so this pack is made for people on low end systems

the original Description

"This modpack integrates the Prehistoric Nature mod, plus its dimensions, and the TreeChopper mod and a few extremely basic support mods added.  Plants which still exist now are set to spawn in the Overworld. We've bundled in an optional texturepack which you might like to play with. If you need Optifine, you need to add that manually. 

to run this pack on For optimal performance use 4gb ram or more

optifine
there should be no issue using optifine in this modpack"