If you've got USD15m to play with the world is your oyster. F900EX, CL604 are both within your reach and should make your mission profile.
H4000: Value will most likely drop like a stone. If you are going to pursue this option further get one that's had the block point upgrade done. Oh, and there's not many EASA certified ones out there.
F50EX: Bit of a dinosaur compared to the HA4T and CL30 but a lot of aeroplane for the money - and as long as you use it fairly regularly it'll outlast the cockroaches. I've seen some dipping under $5m.
CL30: Holding value very well, and a good amount to chose from. Again, a lot of aircraft but not nececerally good value.
You haven't mentioned the G200 which is nicely in your budget and will also meet your mission requirement.