Italys reputation in WWi tends, IMHO, to suffer from back projecting WWII in to the prequel (something not unique to Italy). With better preparation and critically better leadership I think that Italian performance in the Izonzo (or wherever elee) could have been more obviously decisive.
As a possible divergence let's take a personal favorite and say that Alberto Pollio survives into the war itself. Italy still enters the war on the Entente side, but does so after a year of studying the western front and amassing material, and better command. One of the key shortcomings was Cadornas tendency towards massed frontal assaults, combined with a complete lack of adequate equipment. TTL they have better leadership and presumably better tactics as well as better gear, and as a consequence Austria collapses completely under the Brusilov offensive in 1916.
The bigger issue is that a negotiated peace in 1916 (if at all possible) is going to be very different- the Arab Revolt is basically a non starter, and Germany is still sitting on a lot of key french territory. TBH I feel that Italy staying out in 1915 probably has her not joining the Entente at all; I can believe that a relatively austrophile Chief of Staff does not meaningfully delay her entry in 1915, even if it results in a limited breakthrough at the Izonzo- up to Ljubjana seems at the limit and that's pushing it. Still with Trieste in Italian hands and part of the Carnian ridge I suspect Italy could withstand a german counteroffensive a la the Piave, even if forced back to the Izonso itself.
At this point of course the Western front starts coming into play, And the question of whether Germany could force a status quo any in Europe. Woild Britain stick it out for Alsace and a Tsarist claim to Prussia and the Straits? Alternately I suppose Germany could be allowed Austria (sans south tirol) in return for the corridor and Alsace. This would probably require a republic.