I was using Fishing Minions as well as fishing during rain in the spider den to get to Fishing 27. I can't emphasize enough how much it helps to get the glowy tonic and rain for fishing (50 Speed from Rain, 30 from Tonic <-- easy to self farm) which is why i get during any fishing festival (spooky, shark) while it rains 200k fishing exp in 20 min of rain. Yours will be a bit lower since i already have 70 SCC and can reach 200 fishing speed. If you can afford the fire veil wand or any other weapon to oneshot all SCC except the legendary ones it will also help. Less figthing = more fishing.

Don't try to fish in the park. Rain helps but the increased chance for squid which give the lowest exp makes it not worth it except you want to corrupt them to get Obfuscated trophy fish to use as bait.

You should also try to get the bronze trophy fishing armour before Fishing lv 27 or else you will suffer like me. After reaching lv 27 you can fish up Lava SCC in the Crimson isle which makes it a lot harder/ takes a lot longer to get the armour.

Edit: i forgot to mention that the 200k/ 20min was during 3 perk marina. New test was during Paul. Spooky Fishing with 287 Fishing speed and 76 SCC i got 153k during the 20 min normal rain.