In Medea, are lines 1080-1115 considered a choral song (even though they do not possess the usual strophe/antistrophe structure)?

Yes, these lines 1080 to 1115 are sung by the chorus, though these lines do not exhibit the characteristic strophe/antistrophe structure. The chorus (though a corporate body made up of a group of individuals) played the role that a narrator would in a modern play; its job was to inform the audience of elements such as backstory, context, or activity happening offscreen (as the audience was often spared the gruesome action of a play). But apprising the audience was not the only role of the chorus; it was also the chorus' job to urge other characters to do things (as occasionally the chorus does in Euripides's Medea). The chorus may be male (as in Sophocles's Antigone and Aeschylus's Agamemnon) or female (as in Euripides' Medea and Hippolytus). Scholars often discuss the different functions of an (ideal) male chorus and a (passive) female chorus.
The structure of a choral piece is a strophe followed by an antistrophe (which translate to "turn" and "turning back," respectively). Occasionally, there is a third piece added, called an "epode," which exhibits a slightly different meter, as is often omitted. This overall structure taken together is called a "stasimon." "Stasimons" (strophe-antistrophe pairs sung by the chorus) alternate with "episodes" in which one or more characters address the audience.
In Euripides's Medea, lines 1080-1115 are where the stasimon is expected from the chorus. Because this portion does not meet this structural expectation, these lines are sometimes called "astrophic." Other editors call this an "anapestic interlude," because the feet are anapests (two short feet followed by a long one). Suffice it to say that these lines represent a changes in the typical alternation between stasimons and episodes. This exceptional structure demonstrated here in Euripides' Medea likely owes to the unique subject matter. In the lines immediately preceding these, Medea has resolved to kill her children. Within these lines, the chorus rather surprisingly claims that children are invariably difficult for parents, who are forced to care for and worry about their children incessantly. On top of these burdens, claims the chorus, is the risk that one's children die (as will be the case with Medea's). Rather than (as elsewhere) the chorus dissuading Medea from killing her children, here, the chorus proclaims how difficult children are.