Alright guys, I have some good news and I'm glad to tell you, that it wasn't (in 100%) fault of Mirage. Cause of problems was the mission. After update of DCS from 1.5.3 to 1.5.4 mission got messed up, and it looked like Mirage also didn't receive the update (only in this mission). Solution was to make the mission from total ZERO, from the basics. I reworked the mission from 1.5.3 to current version, and now it looks the same as it was before, but it's compatible with current version. Mirage can fly now like 700 knots on low altitude, not 750-800 like it was with broken mission, but the missiles still can't hit him, I mean only IR missiles (we didn't try radar guided missiles yet), because now AAA works like it should, and they took me down before I even get closer to airfield. Anyway, today we've tested reworked mission, which provided us a lot of fun, especially in dogfights. Now I have a request for ED team, because reworking a bit more advanced mission every week with every update is gonna be a little tiring, so I'd like to try and ask about implementing something like "further compatibility", I think it shouldn't be a problem, but if it is, so at least information with updates about incompatibility of missions from previous version, because re-saving mission in ME doesn't solve the problem, and I had to rework it, probably the same analogical situation happens on other servers and I'm sure it's not easy to rework mission from, for example 104th Phoenix server where mission has a lot of triggers, units etc.
P.S. I'm not saying that's still M2K's fault, or maybe missiles are somehow broken.