I agree with Jammy. Give TL1 right away and put some demands to get TL2. Then your lurkers will stay at TL1. Problem solved.
A bit or much off topic, but lurkers aren’t any issue. The rule is 99-1 (99% read, 1% create) or 90-10-1 (10% create 90% of all content, and 1% of those create 90% of that content). So it doesn’t matter what perks those who are just reading get, because they never use those things. They are happy users who enjoy when consuming the content and perhaps they are spreading the good word about your forum. But the main point is there is no force to force them create content. That’s why it is just waste of time and energy to even think what TL they should be.