Alchemy can be a high CPU demanding plugin..... It always was and still is.
However, did you adjust the CPU usage for it via it's drop down menu in the top right hand side of the plugin? It's labelled "Quality" and by default it is set to Great.....
Note: Running Logic with only a 32 or 64 i/o buffer size.. can put a great strain on your system.. Try adjusting that to 128 to ease the strain a little.... You probably wont even notice the small amount of additional latency after a short while of usage... I even run mine at 256 at times when using a large number of high CPU usage plugins like multiple copies of Diva for example....