Is there any solution for speeding up the login process when you have a large number of students?
How are you doing authentication (logins) and enrolments (adding people to courses)?
When a user logs in, Moodle checks the login details then checks which courses they are enrolled on. This can take its time.
I do enrolments through an external MySQL database. Before, it took 10 seconds to check which courses a user is on in the database (we have 750,000 enrolments records). I optimised our database, and it now takes 0.2 seconds. Login time improved accordingly.
1500 is not that many at all.
So, what makes you think your performance problem is tied to the amount of users you have?
I think as Visvanath pointed out, you should try some general performance improvements.
The comments about an external enrolment DB are just that, they are for managing your enrolements and not your actual student data inside Moodle. Moodle won't be reading from it in the general course of operation, but will sync from it on a regular basis.