Every web developer will tell you your site needs a redesign, because redesigns are what we sell. So let me be useful instead and give you the framework I use to talk clients *out* of rebuilds about a third of the time.
Most Indian businesses discover website maintenance the same way: something breaks, they call the developer who built the site eighteen months ago, and the developer either does not respond or quotes a number that feels like a pen
The first thing I do on any speed complaint is ask the client to open their site on their own phone, outside the office, on mobile data. There is usually a pause, and then: "that's much slower than I thought."