Yes, you should have inline fuses of the correct amperage for each instrument.

But bear in mind that your 15-amp fuse was installed to protect that circuit - and blew. So the wiring for the circuit is almost certainly undersized for the combined draw you plan to place on it, and if it blew at 15 amps and you plan to run 22 amps through it, you may not trip the fuses but you may set your boat on fire.

The connections at the electrical panel on your 1986 boat (unless recently replaced) are also likely corroded, so that further reduces the ability of the wire to carry the amps you want.

Nothing wrong with having a 25-amp fuse for "instruments" or whatever, in the electrical panel, or better yet, a breaker, so long as that leads with a fat wire to a bus block, from where you take off individual wires of the right gauge (+2) with the fuses you need for your instruments. I would not use the existing wire and simply split into three leads with fuses.

It cannot be said loud enough or often enough. The fuse or breaker is there TO PROTECT THE WIRE!!!!!! NOT THE INSTRUMENT. if the existing wiring was installed with a given size fuse (and that size was determined based on wire size and length) then you risk setting the wire on fire by putting in a larger breaker.  Even if you split at the breaker with runs from there to each instrument you risk burning the wire which feeds the breaker. There are others who routinely contribute to this site that can speak very eloquently and technically on this subject. Getting the advice of an experienced marine electricien is definitely a good idea in this case

On Island Girl a  Blue Seas  breaker was added near the electrical panel and large wiring (6 gauge) back to the aft blukhead. There was added a Blue seas fuse block. From there each item has it'd own fuse and wiring. Radar, Auto pilot, Chart plotter, I-70. I asked the Marine electronics tech about why such a large CB and wire. He said with the newer electronics you want very stable power. Line loss/voltage drop is what he was worried about.
 

I have an '87 and need to diagnose a failure in one of the instrument light circuits on my binnacle.The other instrument lights work so I figure it is a broken wire or at the split.  I know this is not exactly the topic here but I figured as long as we are talking instrument wiring someone might be able to tell me where the wiring harness splits for the binnacle mounted instruments.  thx.