Q. In case of need, as the son traveling from far, is in town only on that day, can you arrange a matzeiva unveiling on Tu Beav? (15 of Av).

A. Our Sages teach that there were no greater Yomim Tovim in our nation as the Fifteenth of Av and Yom Hakippurim. (Taanis 26b, Bava Bassra 121b). Therefore, Shulchan Aruch (O.H. 131: 6) rules that Tachanun is not recited on this day.
Poskim mention that one should avoid a ceremony of dedication or hakomas hamatzeiva on Tu Beav, at least when possible, since no hespedim and eulogies are said on this day, which is usually part of the dedication ceremony or the reading of the matzeiva. (Minchas Yitzchok 3: 51-52, Kinyan Toiro 3: 43).
Horav Shlomo Miller’s Shlit’a opinion is similar.

Rabbi A. Bartfeld as advised by Horav Shlomo Miller Shlit’a