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OK, let's see at the data points. You are using the same version of Kickstart that used to work before. The code has not been modified. You are using a backup archive that is roughly the same size and has roughly the same number of files. Therefore the same code working on a roughly similar archive will always run at roughly the same speed. After all, the only thing that is limiting Kickstart's performance is the speed of PHP itself, the disk I/O speed and the CPU speed. None of that are part of Kickstart... but they are part of your hosting environment.

Considering that you are using PHP 7.2 which is blazing fast we can rule out the PHP version as being a performance limiting factor (PHP 7.2 is 2x as fast as 5.6 which is, in turn 2x to 3x as fast as 5.3).

So the only thing that may have changed is disk I/O and CPU speed. Your host has either moved your account to a slower server OR the server is now more crowded OR they are enforcing resource usage limits. Of course they will deny everything but that's how all hosts work. That's how a host can afford to sell you a hosting package with plenty of a space and bandwidth at a fraction of the price it would cost you to get a similarly configured physical server at a data center.

FWIW a backup archive at 58MB takes less than 30" on my mid-spec virtual private server (roughly the performance of a Skylake i5 with a run-of-the-mill Kingston SSD -- I know that because that's the spec of my older dev machine that was running at the same speed as my server). 2-3 minutes for a cheap shared host sounds about right. 15 minutes is way too much unless we're talking about sub-$5/month hosting, in which case it's a very crowded server, so yeah. 50 minutes is slower than FTP'ing the files. So, clearly, the hosting is the issue here. Sorry :(