It is recommended for the 360 that you actually install the Discs before running them. The load times are even worse on PS3. Only the PC was patched to fix loading issues.
It is just one of the hurdles we have now. As games become bigger and more complex and the hardware is pushed more. Not having a new generation of hardware means longer load times for big games.
Unfortunately installing the game is all you can do. If you have a HDD on your 360 that is. Other then that I recommend a good handheld or something to distract you while you wait for loads.
Deus Ex is a really good game and worth the annoyances to see it through to the end.