You may need to reduce speeds to the lowest avaliable system you want to support Loading Speed wise.
Hoever; 10 seconds is probably unacceptable. Id say more than 1/2 a second is likely not acceptable…
The old system manages loading a streamed level with billions of foliage in like .25s on an older CPU.
Some of it you need to fine tune (because cpu limits), but some of it is probably unacceptable in the current state…