I have a 3-9x40 vortex crossfire II scope it doesnt have a adjustable ao on it would this be ok to put on my 15 22 or not?

Parallax becomes an increasingly large problem as magnification increases and 9x is about the point where it starts to be an issue.

Properly mounting the scope so that your eye is naturally centered on the axis of the cone of light produced by the scope will reduce the error.

A contributing factor is the distance the scope is set at to be parallax free. Most center fire scopes are set up to be parallax free at either 100 or 150 yards, while most rimfire scopes are set up to be parallax free at 50 yards. I believe Vortex uses 100 yards on that scope, so it's not bad for a .22 LR that will do dual short and long range duty.

If you are doing long range shooting with a precision .22 LR, the 100 or 150 yard parallax works well. For short range shots, just dial the magnification back to 3 to 4x and the parallax error will be minimal.

How far do you plan on shooting? BB57 has supplied some excellent info. I do more steel/multiple target shooting and don't shoot much further than 75 yds. with my 15-22. I use a TruGlo Omnia 4, It's a 1-4x24mm. They also make an Omnia 6 which is a 1-6x24. It has an illuminated reticle with hold-overs. Although it's calibrated for 5.56/.223, it still works well for .22lr. Great scope for around $220.00 and comes with lens covers, 1 piece mount, target turrets, and throw lever. Something you might want to consider.

(I put an Atibal QD 1 piece mount on mine)

I bet you're scope will work fine. I wanted to go small and .22lr specific so I am using a Nikon 2-7x32 P22. Similar to the P223. Around $120 new and $75+ used.

Same here. I think Nikon has renamed the P-22. Great scope for 15-22. Get the Nikon mounts also.

I went with a Primary Arms 1-6X scope they made specifically for .22LR. If you are going to use it for hunting, I've found that sometimes 3 or 4X for the low end on a hunting scope to be too much for some shots.