Pembroke’s Eimear Mullen starred with the ball in the win over Essex, as she took 3 for 11 to restrict them to 85 for 5.
Opener Maha Rana carried her bat in an unbeaten 47, hitting five fours and one maximum.
Ali Keenan (1-7) and Isobel McCormack (1-12) were the other successful bowlers for the Irish.
The Irish chased down their target with 9 balls to spare – thanks primarily to Merrion’s Emma Paul who hit 7 fours in a top score of 36.
Skipper Orla Prendergast (17*) and Louise Little (12*) ensured the morale boosting seven-wicket win.
Lancashire however proved too strong for Ireland, with Daisy Mullen hitting 7 fours and 3 sixes as the English county posted 115 for 7.
The Irish fielding held up well as they managed three run outs – Louise Little (2-21) the most successful of the bowlers.
Katie Hodge then ripped through the Irish top order as she claimed 4 for 7.
Instonians Amy Hunter launched a fightback as she thumped 5 fours in a top score of 28, sharing a stand of 50 with Isabel Saeed Maguire (15) but the Irish finished 23 runs short.
IRELAND UNDER 15 GIRLS AT THE MALVERN FESTIVAL
At Malvern College, Ireland U15 Girls lost to Lancashire U15 Girls by 23 runs.
LANCASHIRE 115-7 (20 overs; D Mullen 63, L Little 2-21)
IRELAND 92-6 (20 overs; A Hunter 28, I Saeed Maguire 15, K Hodge 4-7)
At Malvern College, Ireland U15 Girls beat Essex U15 Girls by 7 wickets
ESSEX 85-5 (20 overs; M Rana 47*, E Mullen 3-11)
IRELAND 86-3 (18.3 overs; E Paul 36)