Yes, at the early stage of KTS it was slow (in 2019). But from my testing on a new project (AS 4.2beta02 + Gradle 6.7.1 + all are KTS scripts), it was not too bad, it took around 800-1000ms for auto-complete popup after keying a letter like “c” for classpath. My machine is using Intel i7-7700 with Xmx4g config