D&D levels of magic in every edition just do not map to the 3rd Age very easily. Arguably they sort of work for the early 2nd Age.

I would put the non-hobbit fellowship members at highish single digit levels, while Gandalf himself shows no reason to guess he has more than 4-5 wizard levels of spellcasting. Gandalf does have significant other forms of power to draw upon, so his ECL could easily at the upper range of single digit level.

Tolkien works very hard to shield the reader's eyes from overt examples of strong magic. In the Hobbit, Gandalf shows some skill at manipulating fire in the Hobbit against the worgs, but that is 3rd level spell caster kind of stuff. In FotR, there is a great battle between Gandalf and multiple riders at Weathertop before Aragorn/hobbits get there, whose scope is hinted at by the evidence of the aftermath.

The most overt example of powerful magic we readers ever observe is the breaching of the gates of Minas Tirith by means of an insane battering ram with some magical assistance from the Witch King. Even that is beautiful theater more than logical necessity, as no one would be confused by a big arse battering ram breaching a gate after a few additional hours or days of effort.