Yes, but he's talking about his rifle not your old girlfriend Annie, Annie grab my fanny!What you call 'loose' I call 'well loved'
A good shimming trick I learned is to use JB weld. Grease up one side of the surface and use that painter's tape over the exposed surfaces of all neighboring parts. Clean the surface you want to build up. Spread a small amount on that surface. Use spring clamps or rubber bands to hold it in the position where it will make the most gap. Usually wait a bit on the JB weld and let it get a little thick before doing. Sorta like bedding a stock of a rifle.Like PSLMAN, my ArmaLite M15A4 handguards are loose. I put strips of electrical tape under the front tabs that help a lot but need a permanent solution. The RRA handguards from PK Firearms sound interesting. I've also heard that Noveske has an even better middy handguard and that G&R Tactical has some heavy thermold type middy handguards as well that are high quality.
Of course we're assuming the OP's M15A2 is an ArmaLite middy. Also his idea of JB Weld could work if building up the handguards where they contact the front clips.