Suggestion for soloist w/ orchestra rep for high school competition

Handel and Mozart arias would be fine - but I'm wondering whether that
"maximum 15 minutes" is also implying that the piece should not be too
short, either.

I would still urge you to look into some of the baroque and classical
solo cantatas or solo motets for soprano and chamber orchestra and
continuo (in Italian, English, or Latin), such as:

Handel:
Delirio amoroso: Da quel giorno fatale, HWV 99
Silete Venti, HWV 242
Gloria in excelsis Deo in B flat Major, HWV deest (previously unknown,
rediscovered just a few years ago)

Haydn:
Miseri noi, misera Patria (1790)
Berenice, che fai? (1795)

Monteverdi:
Sonata sopra Sancta Maria, ora pro nobis

Mozart:
Exultate, jubilate, K 165
- Also some of the longer (7-11 minutes) soprano concert arias:
A Berenice...Sol nascente, K 70
Fra cento affanni, K 88
Ah, lo previdi!...Ah, t'invola, K 272
Alcandro, lo confesso...Non so d'onde viene, K 294 v1
Non so d'onde viene, K 294 v2
Popoli di Tessaglia!...Io non chiedo, eterni Dei, K 316
Ma che vi fece, o stelle...Sperai vicino il lido, K 368
A questo seno deh vieni...Or che il cielo a me ti rende, K 374
Mia Speranza adorata!...Ah non sai quai pena sia, K 416
Non piu. Tutto ascoltai...Non temer, K 490
Ch'io mi scordi di te?...Non temer amato bene, K 505 (written for
Nancy Storace, the first Susanna, the tessitura is a bit lower than
the others)
Bella mia fiamma, addio!...Resta, o cara!, K 528
Ah se in ciel, benigne stelle, K 538

Vivaldi:
Canta in prato, RV 623
In furore giustissimae irae, RV 626
In turbato mare, RV 627
Longe mala umbrae terrores, RV 629
Nulla in mundo pax, RV 630
O qui coeli terraeque, RV 631
Sum in medio tempestatum, RV 632
Vos aurae per montes, RV 634

Alessandro Scarlatti:
Su le sponde del Tebro, D 2364

Pergolesi:
Salve Regina in A minor

Telemann:
La Tempesta: No non turbarti, TWV 20:42

Arne:
Morning (1755)
The Lover's Recantation (1761)

Mendelssohn:
Salve Regina in E flat Major