How many apps can be installed in a smartphone before it slows down?

I got a cheap phone with 1gb ram,4gb internal memory,running Kitkat I can't install more than 20 apps before it crashes, have to transfer my whatsapp videos to PC every other day when it says "Out of space" even tho I got 32gb microSDcard and all media is stored in card by default not internal memory, card has abt 20gb free space.

I have heard that only android slows down over time,is that true?Coz one of my friends got a Lumia with 512mb ram but has around 60apps and it takes time to load with some animations but it never slows down/crashes. I have no idea abt iphones.

How many apps[for lets say 50mb each] can I install before it slows down/browser crashes when opening a site with lot of pics?

a)ANDROID Samsung Galaxy s6 3gb ram,32gb internal storage phone?
b)Iphone 6s 2gb ram,16gb internal?
c)Windows lumia 930 2gb ram,32gb internal?

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