If you are on ASE 15.0 you can't stop it. The license information is stored persistent in "I can't tell which table". You need to build a separate license server as soon as possible. I find the whole SYSAM 2.0 feature pretty screwy, as it puts added maintenance pressure on Sybase customers.
Your performance issues are perhaps unrelated to license feature. The license check is done every 15 mins by ASE or whenever the engines are 60% idle.