Comparisons of different VMS solutions is really challenging.
We have tried it in the past, you start off with a spreadsheet of features and before you know it you have a huge grid.
The best thing to do is to take advantage of the free trial downloads that the manufacturers provide and take (at least) a shortlist of possible solutions for a test drive and see which you like.
They also vary greatly in cost.
And, with most, the more cameras that you add the higher up their solution offerings you need to go and the more expensive the solution per camera cost will be e.g.
Milestone Systems.
Luxriot offer good value.
Vivotek's VAST software has always been appreciated for its user-friendliness (intuitive in everyday use).
NB - Any prices are per licence, and you will have to install one VMS base licence per physical (or VM) server.
Also, it is common for VMS software from a camera manufacturer to allow you to add their own brand of cameras free-of-charge, but to charge a fee for an open camera licence to add third-party brand cameras - for example, for each say Hikvision camera that you want to add to Vivotek's VAST software you will need to pay approx. a £40 licence fee.
You will not manage/record 1,500 cameras on any single server.
So, far from straight forward, and many more options than I have mentioned ...
Also, if you have a requirement for a control room monitor wall (and operator desks) make sure that you get that factored into your specification from the very beginning.
Likewise if you need multi-user access and permission controls.
And also if you need access from mobile phones ...
