May 15 (Eastern Orthodox liturgics)

• The Seven Apostolic Men, Martyr Bishops, ordained in Rome by Saints Peter and Paul and sent to evangelize Spain (1st century):

• Saints Torquatus, Ctesiphon, Secundus, Indaletius, Caecilius, Hesychius, and Euphrasius[1][2][3]

• Saint Achillios, Bishop of Larissa (330)[4][5]
• Saint Pachomius the Great, founder of cenobitic monasticism (348)[6][7]
• Saint Silvanus of Tabennisi (in the Thebaid) (4th century)[8]
• Saint Barbarus the Myrrh-gusher of Greece (c. 820 - 829)[9]
• Saint Panegyrios of Cyprus (Panigerios, Panegyrius), Wonderworker of Malounta[10][11][note 2]

• Martyrs Cassius, Victorinus, Maximus, and their companions, in the Auvergne in France (c. 264)[2][3][note 3]
• Martyr Simplicius, Bishop, in Sardinia (c. 284-305)[2][3][12]
• Virgin recluse Caesarea of Otranto[3]
• Saint Hilary of Galeata (Hilary of Tuscany), founder of the monastery called Galeata, later known as Sant'Ilaro (Sant'Ellero di Galeata) (558)[3][13]
• Saint Colmán of Oughaval (Colman mac Ua Laoighse, Colman Mc O'Laoighse), a disciple of St Columba and St Fintan of Clonenagh (6th century)[3][note 4]
• Virgin-martyr Dymphna of Geel, Flanders (c. 650)[2][3][14][15][16]
• Saint Waldalenus, founder of monastery of Bèze in France (7th century)[3]
• Saint Bercthun (Bertin), a disciple of St John of Beverley and first Abbot of Beverley in England (733)[3]
• Saint Bertha of Bingen (c. 757), and her son Saint Rupert of Bingen (732)[3]

• Saint Isaiah of Rostov, Bishop and Wonderworker (1090)[17]
• Saint Isaiah of the Kiev Caves, wonderworker (1115)[18][19]
• Saint Andrew the Hermit, of Mt. Kalana, Epirus, wonderworker (c. 1237 - 1271)[14][20]
• Saint Pachomius of Nerekhta, abbot (1384),[21][22] and Saint Silvanus of Nerekhta (1384)[23]
• Saint Euphrosynus of Pskov (Eleazar), abbot and wonderworker (1481)[24][25]
• Saint Serapion of Pskov, disciple of St Euphrosynus of Pskov (1481)[26][27][28][note 5]
• Saint Pachomius of Keno Lake Monastery (1525)[29][note 6]
• Saint Demetrius of Moscow the Wonderworker, Slain Crown Prince (1591)[32]
• Saint Arethas of Valaam and Verkhoturye (1903)[14][23]

• Discovery of the revered icon of Kamoulianos "Acheiropoieta" ("made without human hands").[36][note 8]
• Translation of the sacred relics of the Holy Apostle Titus of Crete, from Venice (which had taken the relics in 1669), back to the Greek Orthodox Archdiocese of Crete (1966)[37][38]
• Uncovering of the relics (1846) of Saint Tikhon, Bishop of Voronezh, wonderworker of Zadonsk (1783)[39][note 9]

• 
  Sts. Achillius of Larissa and Pachomius the Great.
• 
  St. Pachomius the Great.
• 
  Stained glass of St. Cassius of Clermont.
• 
  Chair of Saint Hilary of Galeata, in the cell in which the saint used to pray.
• 
  St. Bertha of Bingen.
• 
  St. Euphrosynus of Pskov.
• 
  St. Dmitry of Uglich.
• 
  St. Dmitry of Uglich.

• May. Self-Ruled Antiochian Orthodox Christian Archdiocese of North America.
• May 15/28. Orthodox Calendar (PRAVOSLAVIE.RU).
• May 28 / May 15. HOLY TRINITY RUSSIAN ORTHODOX CHURCH (A parish of the Patriarchate of Moscow).
• May 15. OCA - The Lives of the Saints.
• Complete List of Saints. Protection of the Mother of God Church (POMOG).
• May 15. Latin Saints of the Orthodox Patriarchate of Rome.
• May 15. The Roman Martyrology.

Greek Sources

• Great Synaxaristes: (in Greek) 15 ΜΑΪΟΥ . ΜΕΓΑΣ ΣΥΝΑΞΑΡΙΣΤΗΣ.
• (in Greek) Συναξαριστής. 15 Μαΐου. ECCLESIA.GR. (H ΕΚΚΛΗΣΙΑ ΤΗΣ ΕΛΛΑΔΟΣ).

Russian Sources

• (in Russian) 28 мая (15 мая). Православная Энциклопедия под редакцией Патриарха Московского и всея Руси Кирилла (электронная версия). (Orthodox Encyclopedia - Pravenc.ru).
• (in Russian) 15 мая (ст.ст.) 28 мая 2013 (нов. ст.). Русская Православная Церковь Отдел внешних церковных связей. (DECR).