Originally Posted by Neverender
Already confirmed this, but forgot to update the roadmap. Thanks for pointing this out!
Also make sure to update the guide for that achievement.
Also, here's my hints about the 1.5 mil in arcade:
I find the Escalation Spaceship level the easiest to do this in. I got 1.9 mil on my 2nd try, 1.4 on my first try.
A couple hints would be to take advantage of your multiplier early. If you aren't getting almost every gem in the first 20-40 worlds, start over and try again. This will save you a lot of headache in the later levels.
Also, as soon as you complete a level, hold back. The levels sometimes like to randomly start you in front of a wall, or a gem on the opposite side of the screen from you. By holding back, you can do a quick evaluation of the level before it gets started. I found this essential on my 1.9 mil playthrough.