Warmup duration depends on 3 factors:
The number of pages to generate: the first warmups generally contain a lot of pages, which is normal, and this number will decrease with each warmup
The maximum number of bots you've defined: this is 30 by default, but you can reduce it to 5 bots to lighten the server load, but this obviously extends the time of each warmup
Page TTFB without cache: if server response time is long without cache (> 3s), you may need to analyze Prestashop's slowness