Will the number of subscribers of an internet service provider affect speeds?

I'm sorry I really don't know anything about this and I don't even know if this is the right place to ask but here it goes:

We're choosing between 50mbps and 75mbps speeds and I found that 50mbps is sufficient, but my gather argues that we need the 75mbps option since by the time we start classes, there will be a lot of people connected to the internet and I'll eventually have a very slow connection with 50mbps because of traffic or something. Is this true? Considering that I'm talking about maximum speeds through fibr connections and there are more and more people connecting with the ISP per day.