Agree with above posters. In AY-scheme, hitting silver is not very difficult but that will only grant access to lounges connected with AY-flights and no guest. Gold and Platinum take some serious longhauling.
BAEC sapphire/silver and emerald/gold used to be easy to achieve. Their ruby/bronze is good next to nothing. 600 TP:s would require 30 short flights in Y resulting in 20 TP:s each. Those flights need not be Y-lettered (as with AY to get 100% accrual) but also several lower booking classes are recognised. Of those, 4 have to be BA coded annually. 1500 TP:s would be within reach e.g. by monthly shorthauling within EU and having some connecting flights within each of those trips.