Let me give you a useful tip that works me. Maybe only works on me, but I hope this helps you. Whenever you open the launcher, see how fast does the play button becomes available. If it turns orange very fast, that means you are most likely not having lag, if it takes a while to turn orange.. it means you are most likely to lag. Works almost every time for me. Sometimes I re-open the launcher or restart my computer, until the play button becomes orange very fast.