It takes a moment the first time to run ispell, since it has to start up a process, but after that, it's nearly instantaneous. Accept word this time. Replace word with typed-in value. Query-replaced in buffer. Move cursor to original point.
Leaves cursor at the current point, and permits the aborted check to be completed later.
There is an ispell-region command if you just want to check a portion of your file. This can be invoked as a M-x command. We now switch topics to things that you do within latex, particularly customizing it by use of style files. Journals and publishing houses often produce their own style files. LaTeX works as layers of macros on top of the primitives of the TeX language.