Question: The 2015 Ulster Club Senior Football Championship had reigning champions of which Gaelic club?

Context articles: Fermanagh Senior Football Championship
Slaughtneil GAC
2015 Cavan Senior Football Championship
2014 Cavan Senior Football Championship
Gaeil Colmcille CLG
Cork Senior Football Championship
2013 Cavan Senior Football Championship
2015 Ulster Senior Football Championship
Cavan Senior Football Championship
2015 Ulster Senior Club Football Championship

The Fermanagh Senior Football Championship is an annual Gaelic Athletic Association club competition between the top Gaelic football clubs in Fermanagh.
 The winners of the Fermanagh Championship qualify to represent their county in the Ulster Senior Club Football Championship, the winners of which go on to the All-Ireland Senior Club Football Championship.
 The current senior football champions are Derrygonnelly Harps.
Robert Emmet's Gaelic Athletic Club Slaughtneil (Irish: "CLG Roibeard Éiméid Sleacht Néill" ) is a Gaelic Athletic Association club based on the townland of Slaughtneil, County Londonderry, Northern Ireland.
 The club is a member of the Derry GAA and compete in gaelic football, hurling and camogie.
 The club is named after Irish patriot and revolutionary Robert Emmet and play their home games at Emmet Park.
The 2015 Cavan Senior Football Championship is an annual Gaelic Athletic Association club competition between the top Cavan Gaelic football clubs.
 It was first competed for in 1888.
 The winners get the Oliver Plunkett Cup and qualifies to represent their county in the Ulster Club Championship and in turn, go on to the All-Ireland Senior Club Football Championship.
 Cornafean have won the most titles, having been victorious 20 times.
 The 2014 senior football champions are Cavan Gaels who defeated Kingscourt Stars in the 2014 decider to claim their 13th Cavan Senior Football Championship.
The 2014 Cavan Senior Football Championship is an annual Gaelic Athletic Association club competition between the top Cavan Gaelic football clubs.
 It was first competed for in 1888.
 The winners get the Oliver Plunkett Cup and qualifies to represent their county in the Ulster Club Championship and in turn, go on to the All-Ireland Senior Club Football Championship.
 Cornafean have won the most titles, having been victorious 20 times.
 The 2013 senior football champions are Ballinagh who defeated Cavan Gaels in the 2013 decider to claim their first Cavan Senior Football Championship.
Gaeil Colmcille CLG is a Gaelic Athletic Association club located in the town of Kells, County Meath, Ireland.
 The club competes in Meath GAA competitions.
 The club currently plays at senior level in the Meath Senior Football Championship.
 The club was founded in 1964 and had almost immediate success reaching the Meath Senior Football final in 1964 but lost by 3 points to Kilbride GFC.
 In 1966 the club won the Meath Senior Football Championship for the first time and then again in 1968.
 It has won the Senior Football Championship three times, most recently in 1991, and the Meath Intermediate Hurling Championship four times, most recently in 2008.
The Cork Senior Football Championship (currently known for sponsorship reasons as the Evening Echo Cork Senior Football Championship) is an annual Gaelic Athletic Association competition between the top Gaelic football clubs in County Cork, Ireland.
 The winners of the Cork Championship qualify to represent their county in the Munster Senior Club Football Championship, the winners of which progress to the All-Ireland Senior Club Football Championship.
 The current senior football champions are Carbery Rangers who defeated Ballincollig in the 2016 final.
The Cavan Senior Football Championship is an annual Gaelic Athletic Association club competition between the top Cavan Gaelic football clubs.
 It was first competed for in 1888.
 The winners get the Oliver Plunkett Cup and qualifies to represent their county in the Ulster Club Championship and in turn, go on to the All-Ireland Senior Club Football Championship.
 Cornafean have won the most titles, having been victorious 20 times.
 The 2012 senior football champions were Mullahoran who defeated Kingscourt Stars after a replay in the 2012 decider.
The 2015 Ulster Senior Football Championship is the 127th instalment of the annual Ulster Senior Football Championship held under the auspices of Ulster GAA.
 It was one of the four provincial competitions of the 2015 All-Ireland Senior Football Championship.
 Donegal were the reigning champions following the 2014 Championship but lost to Monaghan in the final on 19 July by a point.
The Cavan Senior Football Championship is an annual Gaelic Athletic Association club competition between the top Cavan Gaelic football clubs.
 It was first competed for in 1888.
 The winners get the Oliver Plunkett Cup and qualifies to represent their county in the Ulster Club Championship and in turn, go on to the All-Ireland Senior Club Football Championship.
 Cornafean have won the most titles, having been victorious 20 times.
 The current senior football champions are Ramor United who defeated Castlerahan in the 2016 decider.
The 2015 Ulster Club Senior Football Championship is the 48th instalment of the annual Ulster Senior Club Football Championship organised by The Ulster GAA.
 It was one of the four provincial competitions of the 2015 All-Ireland Club Senior Football Championship.
 Slaughtneil (Derry) were the reigning champions following the 2014 Championship defeat of Omagh St. Enda's (Tyrone)