Yes- the summit of Mount Meru is almost 15,000 feet high. If you climb Meru, you can, with one day or no days in between, climb Kilimanjaro thereafter with a lower number of days (5 or 6) because you will have had exposure to approximately the highest altitude where you will camp on Kilimanjaro (Kibo Hut and Barafu are about 15,500 feet high).
However, do not be too aggressive on either trek. To do Meru and a challenging Kilimanjaro climb back to back may put too much stress on your body. And strenuous activity increases the likelihood of altitude sickness. So while the Meru/Kilimanjaro climb combination can increase the probability of summit success over a lengthy Kilimanjaro climb alone, it can also decrease it. The success of this schedule depends on how strong of a hiker you are.