It depends, to my knowledge / experience not at all if:
- There are enough initial seeds
- They have decent connection / upload speed
So, let’s say when new iso is released we have 10 people (server torrent boxes?) in 
team who are seeding 24/7 - then speed will be top notch from the start, but we still should encourage people to seed after downloading iso, coz more people are seeding - the better speed everyone will get.
Usually first moment low speed problems arise when there’s 1 initial seed, with not so nice speed, once seed count grows exponentially - speed and availability grows as well.
Because basically what torrent does:
- Breaks download to very small chunks which are in turn distributed between seeds
- Then whoever (peer) starts the download - client very quickly ranks and download in parallel all those small chunks from different seeds (usually ranking by availability and speed of seed connection)