There is no official fix for it yet. Unofficial solution is to install ACF 4.3.4 and follow instructions from this thread for patching particular files.
This is not a 100% fix but most of the performance issues are addressed. Read the whole thread before you change any file.
Absolutely do not apply these workarounds on version other than 4.3.4.
Welcome to the Advanced Custom Fields community forum.
Browse through ideas, snippets of code, questions and answers between fellow ACF users