Check your php.ini file and make sure maximum allowed file size is set to at least 1.5GB. To find the location of the php.ini you could create a simple script like this and run it:
Update the file by locating the line like this:
upload_max_filesize = 20M
and change the limit to the desirable size.
1.5GB is rather large. Maybe better just use a FTP program to do the upload.