"The 2015 return is important as the Rosetta spacecraft is orbiting the comet, however it
is not a particularly good one as the comet is an early morning object. If it
behaves as at previous apparitions it will be brightest some 40 days after perihelion,
when it might reach 9th magnitude. The comet was observed by Juan
Jose Gonzalez on August 19 from a high mountain site, when he estimated it at 12.2 in his
20cm Schmidt-Cassegrain. This is fainter than expected, which may have implications
for the in situ science.
The visual and electronic observations received so far (68) give an uncorrected
preliminary light curve for the 2015 apparition of 10.0 + 5 log d + 7.7 log r, though a linear curve peaking 40 days after perihelion fits
the data better."
https://www.ast.cam.ac.uk/~jds/per0010.htm#67P
It came to perihelion on 13 August 2015.[10][11] From December 2014 until September 2015, it has an elongation less than 45 degrees from the Sun.[30] On 10 February 2015, it went through solar conjunction when it was 5 degrees from the Sun and was 3.3 AU (490,000,000 km) from Earth.[30] I